Conventional hydraulic presses have been used to insert hollow axle tubes into differential housings in constructing rear floating axle assemblies for trucks and other heavy-duty commercial vehicles. These axle tubes have a flange for mounting a stationary housing of the wheel hub assembly thereto which must be accurately located with respect to the differential housing. During vehicle operation, an axle half-shaft received in the axle tube transmits torque from the engine to the vehicle wheel turning the wheel and thereby moving the vehicle.
If each mounting flange is not properly located relative to the differential housing when assembly is completed, the axle assembly may be rejected, significantly increasing manufacturing costs. Even worse, if an axle tube with an improperly located mounting flange is put in service on a vehicle, it can result in expensive warranty repairs to replace excessively worn or failed components, particularly since these vehicles are quite expensive and can carry lengthy warranties of 50,000 miles or more.
Should a floating axle assembly with an improperly located flange be assembled to a vehicle, the flange mislocation can cause vehicle wheel misalignment, negatively affecting vehicle ride and tire wear while undesirably increasing vehicle maintenance. Vehicle wheel misalignment can also cause undesirable loading on the axle and wheel hub assembly possibly leading to premature failure and possible warranty repairs that are undesirable since the vehicle manufacturer typically has to pay for the repairs.
If the mounting flange is located too far away from the differential housing, the brake assembly of the wheel may rub against the stationary housing of the wheel hub assembly mounted to the axle tube mounting flange causing undue premature wear of the brake assembly or fire during vehicle operation. If the flange is located too close to the differential housing, it can produce too large of a gap between the brake assembly and the stationary wheel housing leading to excess contamination inside the brake assembly.
During assembly of these axle assemblies, the hydraulic press forces one end of the axle tube into a complementary opening in the differential housing. So that the axle is firmly and permanently pressed into the housing, the axle tube opening in the housing is sufficiently smaller than the outer diameter of the axle tube to provide a tight interference fit when the tube is inserted. Unfortunately, inserting each axle tube into the differential housing to the proper depth to achieve accurate location of its mounting flange relative to the differential housing can present considerable difficulty, particularly using conventional methods and press equipment.
Two problems typically exist that can lead to the mounting flange being mislocated with respect to the differential housing. The first problem is that the position of the flange on the axle tube can and does vary from part to part. Therefore, unless the depth of insertion of the tube into the housing is precisely controlled to accommodate any variation in the position of the mounting flange on the tube, the flange will also be mislocated with respect to the differential housing when assembly is completed. Unfortunately, since the force required to insert the tube into the differential housing is so great, this mislocation cannot be prevented by simply engaging the flange with the press and inserting the tube into the housing until the flange is properly located relative to the housing because the press would damage or destroy the flange. However, in typical practice, these conventional presses simply ignore the mounting flange mislocation on the tube and insert each axle tube into the differential housing a pre-determined fixed distance, usually approximately 3 to 4 inches, resulting in the flange also being mislocated relative to the housing.
The second problem is that, during assembly, the force needed to insert the axle tube into the opening in the differential housing causes the tube, the differential housing, the axle tube and housing locating and clamping fixtures as well as the press to deflect, further compounding the difficulty in accurately locating the mounting flange relative to the housing. As the tube is forced into the opening during assembly it is compressed, reducing slightly its length making accurate positioning of the flange that much more difficult. When released after assembly, the tube is no longer being compressed by the press and "springs back" to substantially its original length causing the flange to move away from the differential housing during spring-back by a distance approximately equal to how much the tube was compressed during insertion. Also, while the tube is being inserted, the force of insertion causes the press to deflect making it even more difficult to accurately position the mounting flange.
In the instance where a pair of tubes is inserted into a differential housing substantially simultaneously, deflection and/or shifting of the axle tube and differential housing fixtures can also occur if the force required to insert each tube into the differential housing is not substantially the same for both tubes. If deflection and/or shifting is not offset, it can result in a further source of mounting flange mislocation.
Additionally, the amount of deflection increases as the force needed to insert the tube into the housing increases. Furthermore, since the amount of force needed to insert the tube varies from tube to tube and housing to housing, it becomes a very complicated matter, indeed, to insert the tube the proper distance into the differential housing tube opening such that the mounting flange is accurately located with respect to the differential housing.
Therefore, unless these deflections are taken into account, mislocation of the flange during assembly can also occur. Moreover, if two or more such errors in locating the flange occur, the errors can aggregate to increase the total amount of mislocation of the flange thereby raising the likelihood that the axle assembly will have to be scrapped. Unfortunately, conventional hydraulic presses do not adequately compensate for these mounting flange positioning difficulties making them increasingly less well suited to manufacture axles requiring ever greater precision of assembly and increasingly more accurate location of its mounting flanges.